The present invention relates generally to error compensation particularly advantageous to high quality signal processing apparatus such as video recording and/or reproducing apparatus.
Waveform distortion resulting from the inherent nonlinear characteristics of analog electronic circuitry is of primary concern to the design of high quality signal processing systems. In video recording, the waveform distortion is accounted for not only by the nonlinear characteristics of frequency modulators and demodulators, but by DC drift and clamping voltage deviation which combine to produce a waveform different from the original. Such distortion problem becomes serious when it is desired to record a signal of high information density such as broadcast satellite television signals. It has been proposed to record such a high density video signal by splitting it into two channel components at alternate horizontal lines and expanding them on time scale twice as longer than the duration of the original in an attempt to relax the high quality requirements. If the separated video channels are affected differently from each other on passing through respective analog electronic circuits, horizontal lines are likely to appear to flicker on the video screen.
Co-pending U.S. patent application Ser. No. 763,604, filed Aug. 8, 1985 by T. Bannai et al, discloses a signal processing circuit for high quality video signal recording and reproduction. This circuit comprises a reference inserting circuit for inserting a ramp waveform at periodic intervals into an analog information signal during a recording mode. The amplitude of the ramp varies linearly as a function of time so that the instantaneous amplitudes of the information signal correspond to those of the ramp and can therefore be represented by the length of time from the start of the ramp. On playback, the inserted ramp is detected by a reference detector from the information signal. A transfer circuit is provided having a transfer function describing the relationship between the original reference waveform and the detected reference waveform which has been affected by errors present in the apparatus in the same manner as the waveform of the information signal. The transfer circuit transforms the waveform of the information signal according to the transfer function to compensate for such errors.
However, if the detected ramp is severely contaminated with random noise, or distorted differently from the manner the information signal is distorted, the error compensation is likely to result in the generation of an information signal which is not replica of the original signal.